Various electric vehicle steering systems have been proposed which steer steerable wheels with an electric motor according to an input from a steering wheel while taking into account various conditions of the vehicle at the same time, and an example of such "steer-by-wire" steering system is disclosed in Japanese patent publication No. 63-332122 filed by the assignee of the present application.
According to such a steering system, the angular displacement of the steering wheel is detected by a sensor as an electric signal, and an electric motor is actuated according to this electric signal. Typically, the steering angle of the steerable wheels is increased for a given input from the steering wheel when the vehicle is travelling at a relatively low speed, and the steering angle of the steerable wheels is reduced for a given input when the vehicle is travelling at a relatively high speed so that the maneuverability of the vehicle at low speed and the stability of the vehicle at high speed can be both ensured. Furthermore, the freedom of vehicle design can be much improved because there may be no mechanical linkage between the steering wheel and the actuator for actuating the steering mechanism, as opposed to the more conventional steering system in which the steering wheel is mechanically coupled with the steering mechanism. Also, various undesirable problems such as an excessive kick-back to the steering wheel, shimmy and judder can be avoided.
However, according to such a steering system, since the response properties of the electric motor and the vehicle response directly affect the handling of the vehicle, the operator of the vehicle who is familiarized with vehicles equipped with more conventional steering systems may have some difficulty adjusting himself to the behavior of the vehicle equipped with a powered steering actuator. In particular, the reaction force acting upon the steering wheel of the conventional steering system is quite important for the vehicle operator as it offers useful information on the behavior of the vehicle, but the prior "steer-by-wire" steering system does not offer any such reaction force, and the operator familiar with more conventional steering systems may experience some difficulty in making proper and accurate steering maneuvers.